1. Field of the Invention
The present invention relates generally to a tensioner for applying a tension to a timing chain or a timing belt used for driving a camshaft of an automobile engine, and more particularly to a tensioner provided with a plunger stopper mechanism.
2. Description of the Related Art
FIGS. 4A and 4B illustrate a conventional tensioner used with a timing chain for transmitting a power between a crankshaft and a camshaft of an engine. The tensioner includes a tensioner body A and a plunger C urged by a spring B to project outward from the tensioner body A. The tensioner body A has a radial pin hole A1 formed therein, and the plunger C has an annular stopper hole C1 formed circumferentially in an outside surface thereof. The annular stopper hole C1 is aligned with the pin hole A1 when the plunger C is forced into the tensioner body A (refer to the Japanese Patent Laid-open Publication No. HEI-7-42804).
When such a tensioner is mounted on an engine, the plunger C is pushed inside the tensioner body A to such an extent that the pin hole Al is aligned with the annular stopper groove C1, and a stopper pin S is inserted through the pin hole A1 into the stopper groove C1, whereby the plunger C can be fixed to the tensioner body A. After the tensioner is fixed to the engine, the stopper pin S is removed, whereupon the plunger C is pushed by the spring B out from the tensioner body A to pressure the chain and thus apply a tension thereto.
However, in the conventional tensioner, when the plunger C and the tensioner body A are pinned by the stopper pin S, the front end of the stopper pin S is inserted until it abuts against the bottom of the annular stopper groove C1 of the plunger C. The stopper pin S is able to pin the plunger C to the tensioner body A, however, the annular stopper groove C1 cannot be formed sufficiently deep because of the limitations on the shape and dimension of the plunger C. Accordingly, a sufficient insertion depth, which is required for the stopper pin S to keep the stopper pin S in an operating or stopping position within the annular stopper groove C1, cannot be obtained.
Thus, the conventional tensioner is unable to secure a slip-out prevention of the stopper pin S, or rather the stopper pin S can fall out when subjected to a slight impact and vibrations created during assembly of the tensioner relative to the engine. In such a case, a troublesome assembling work to the engine is unavoidably required.
FIG. 5 illustrates a tensioner that has improved the foregoing problem, in which the plunger C has a radial pin hole C2 formed in a front end portion thereof for the passage therethrough of the stopper pin S, and the tensioner body A has a pin stopper hole A2 and an oblong pin insertion hole A3 formed in diametrically opposite relation in the circumferential wall of a front end portion of the tensioner body A (refer to the Japanese Patent Laid-open Publication No. HEI-8-4861).
The improved tensioner still has a drawback that the pin insertion hole A3, pin hole C2 and pin stopper hole A2 require a machining accuracy sufficient to enable the stopper pin S to be inserted through these three holes A3, C2 and A2. In addition, alignment of these three holes when inserting the stopper pin S increases a burden of work. Further, since an extra pull-out force is required when removing the stopper pin S, the stopper pin S has to be provided with a ring-shaped pull-out portion S1. Thus, the stopper pin S must be provided as an exclusive component for the tensioner.
Accordingly, it is a general object of the invention to overcome the problems associated with the prior art devices.
A more specific object of the present invention is to provide a tensioner having a plunger stopper mechanism which is capable of locking the plunger in position against movement relative to the tensioner body, is able to protect the stopper pin against slip-off even when subjected to a shock force or Impact during assembly of the tensioner to an engine, and can secure smooth sliding movement of the plunger relative to the tensioner body while the engine is operating.
According to the present invention, there is provided a tensioner comprising: a tensioner body adapted to be mounted to a fixed member; a plunger slidably fitted in a cylinder chamber formed in the tensioner body; a plunger spring acting between the tensioner body and the plunger to urge the plunger in a direction to project from the cylinder chamber; and a plunger stopper mechanism having a radial pin hole formed in the tensioner body and communicating with the cylinder chamber, an annular pin stopper groove formed in a circumference of the plunger, and a stopper pin removably inserted through the radial pin hole into the annular pin hole to lock the plunger in an inoperative position in which the plunger is retracted into the cylinder chamber. The radial pin hole is substantially tangent to the bottom of the annular pin stopper groove, and the stopper pin has a side face held in contact with the bottom of the annular pin stopper groove.
In one preferred form of the present invention, the radial pin hole has a center line extending parallel to a tangent to the bottom of the annular pin stopper groove and offset from the tangent toward an open side of the annular pin stopper groove, and the annular pin stopper groove has a depth slightly greater than a diameter of the stopper pin.
With this arrangement, the side surface of the stopper pin is held in contact with the bottom of the annular pin stopper groove. Since the length of a portion of the stopper pin being inserted in the tensioner body through the pin hole becomes greater than the length in the conventional mechanisms, the posture of the stopper pin being inserted is stabilized, and the stopper pin held in its inserted position against removal by the action of a contact resistance created between the side face of the stopper pin and the bottom of the annular pin stopper groove.
In another preferred form of the present invention, the radial pin hole has a center line tangent to the bottom of the annular pin stopper groove, the annular pin stopper groove has a depth slightly greater than a diameter of the stopper pin, and the stopper pin has a front end portion being resiliently flexed to thereby urge the side surface of the stopper pin into pressure contact with the bottom of the annular pin stopper groove.
With this arrangement, the removal or slip-off of the stopper pin is prevented still more securely because the side surface of the stopper pin is urged against the bottom of the annular pin stopper groove by the resiliency of the front end portion of stopper pin being flexed.
It is preferable that when the stopper pin is removed from the annular pin stopper groove and the pin hole to allow the plunger to move in the direction to project from the cylinder chamber by the force of the plunger spring, the annular pin stopper groove is in radial alignment with an open end edge of the cylinder chamber.
With this arrangement, when an engine incorporating therein the tensioner of the invention is operating, a lubricating oil can ooze or leak out from the cylinder chamber to the outside of the tensioner while adhering to the outer surface of the plunger and accumulate in the annular pin stopper groove. The lubricating oil is in turn supplied from the annular pin stopper groove to the slide surface between the cylinder chamber and the plunger to thereby guarantee smooth sliding movement of the plunger.
The terms xe2x80x9ctangent (line) to the bottom of the annular pin stopper groovexe2x80x9d used herein with respect to the plunger stopper mechanism of the tensioner refer to a tangent line that is set on the basis of the bottom of the annular pin stopper groove formed on the circumference of the plunger.
Further, the tensioner with a plunger stopper mechanism of the invention is not only applied to a hydraulic tensioner, but it may also be applied to a ratchet tensioner, or even to a combined ratchet-and-hydraulic tensioner.
And, the tensioner with a plunger stopper mechanism of the invention is able to apply a tension not only to a timing chain or belt used for performing timed driving between a crankshaft and a camshaft of the engine. The timing chain may include a roller chain and a silent chain, and the timing belt may include a toothed belt.